Generally, in order to install a marine structure such as an oil drilling facility or a wind power generation facility on the sea, a stable fixing force for minimizing shake of the marine structure needs. Further, in order to fix a location of the marine structure, an anchor penetrated into the sea floor is connected to the marine structure through a connecting cable. When the anchor is penetrated into the sea floor, a pile descends from the marine structure to the sea floor, and the anchor provided at the lower end of the pile is located at the sea floor and driven into the sea floor so that the anchor is installed in the sea floor.
A suction pile is installed at the ground by using a pressure difference between an inside and an outside of the suction pile, which is generated when a fluid such as water or air provided therein is pumped outwards. The pressure of inside of the suction pile is equal to or lower than a hydrostatic pressure. The suction pile may be used not only at the sea floor but also at the ground below a water surface, which may cause suction. The suction pile penetrates into the surface layer of the ground due to its weight, and then the water contained therein is forcibly discharged using a pump to generate a suction operation. The suction pile is also called a bucket pile.
The suction pile is shaped like a hollow caisson having a cylindrical shape without a bottom plate. However, a cross-sectional shape of the suction pile is not limited to a cylindrical shape. In order to facilitate the suction, the top portion of the suction pile is closed. The suction pile is installed as briefly explained below.
First, if the suction pile is placed on an underwater bottom (for example, the sea floor), a lower end of the suction pile penetrates to a certain depth from the underwater bottom due to the weight of the suction pile. In this state, a suction device such as an underwater pump installed at the top of the suction pile is operated to pump water contained in the suction pile outwards. Accordingly, the interior in the suction pile is depressurized, and therefore, a differential water pressure on the interior and exterior of the suction pile is caused. In this state, the force is in an equilibrium state with respect to the suction pile in a horizontal direction, but a downward pressing force is generated in a vertical direction, and the suction pile penetrates into the ground due to the generated vertical pressing force.
The underwater pump is installed at the top of the suction pile as described above, and on the sea, a worktable is prepared at a barge or a general ship. Here, a crane for installing the suction pile and a location finder for measuring a location under the sea are provided at the worktable. Therefore, if the suction pile is located at an installation location in the sea and then the water in the suction pile is discharged out by operating the underwater pump, a pressure difference is generated between the inside and outside of the suction pile, and the suction pile is driven into the ground due to the pressure difference.
A resistance for preventing the suction pile from penetrating into the underwater ground is determined by a front supporting force applied to the bottom portion of the suction pile and a skin friction force, and if a penetrating force of the suction pile is greater than the resistance, the suction pile penetrates into the underwater ground. The penetrating force of the suction pile is proportional to the pressure difference between the interior and exterior of the suction pile and a cross-sectional area of the suction pile (namely, a square of diameter of the suction pile), but the resistance is proportion to the diameter of the suction pile. Therefore, if the suction pile has a greater diameter, the suction pile may penetrate into the underwater ground with a smaller pressure difference.
In an existing technique in relation to the anchor, in order to install a burying-type anchor with a great supporting force at the sea floor, the sea floor is excavated and the anchor is located at the excavated place, and then the excavated place is filled and covered again with soil. However, this existing method causes environmental pollutions due to excavation and covering of the sea floor.
As another method, a pile is dropped from a barge to the sea floor, and an anchor is provided with the bottom of the pile, where the pile is rotated to drive the anchor into the sea floor. However, this technique is not available at a very deep sea.
Meanwhile, Korean Patent No. 10-0459985 (entitled a suction pile anchor), Related Prior Art No. 1, discloses an anchor which may be easily installed at a deep sea.
Regarding a suction pile anchor installed in the water, a circular hydraulic jack is fixedly installed at the bottom of a suction pile, and a hydraulic line for operating the hydraulic jack is installed through an inside of the suction pile and a top of the suction pile and connected to the hydraulic linkage on the sea. The top of the suction pile is connected to a crane on the sea, and a pipe for discharging water introduced into the suction pile is installed at the top of the suction pile and connected to a pump on the sea. The anchor is coupled to the suction pile by the hydraulic jack, and in a state where the anchor is driven into the sea floor to a predetermined depth, the hydraulic jack operates to separate the suction pile from the anchor. One side of a wire is fixedly installed to the outer side of the anchor.
Since the anchor is attached and installed to the bottom of the suction pile through the hydraulic jack, the anchor may be easily installed, and it is not required for excavating or covering the seabed, which allows installation of the anchor at a deep sea. In addition, since the suction pile and the hydraulic jack may be reused, costs may be reduced.
However, in the above existing technique, if a marine structure is relatively great, the capacity of the anchor should be set according to a pullout resistance of the marine structure, and thus a lot of costs are required for manufacturing the anchor. In addition, due to a great capacity of the anchor, the anchor may not be easily penetrated into the sea floor. In addition, in the above existing technique, the suction pile penetrates the sea floor in a vertical direction, and due to a small contact surface in a lateral direction, a lateral resistance is weak.
Moreover, even though a large-capacity anchor is recently demanded since a buoyance marine structure becomes greater, it is not easy to increase the size of the suction pile due to the limit to capacity of a transportation ship and equipment for suction.